The specific objectives are to determine the possible role of phosphatidyl serine (PS) and other lipids in opiate bining. With the use of such enzymes as phospholipase A2 and PS decarboxylase, opiate binding can be substantially reduced. By the addition of purified brain PS, binding can be almost completely restored, especially after exposure to PS decarboxylase. Since the unsaturated fatty acid released by phospholipase A2 irreversibly destroys opiate binding, the restoration after exposure to phospholipase A2 is only partial. Another phase of the research is focusing on the nature and configuration of the muscarinic cholinergic receptor, which also appears to have a phospholipid requirement. It has been shown that the muscarinic receptor exists in two intraconvertible states and that the conversion may be under the regulation of coordinate divalent metals interacting with essential sulfhydryl groups.